Exporting MakeBazelTarget() in testing.go

Since we are putting conversion tests in the same
package as the module being converted from now on

Test: m bp2build
Change-Id: Ied53589d497fef70bfa11d8f6067459c9a50cd72
diff --git a/bp2build/python_library_conversion_test.go b/bp2build/python_library_conversion_test.go
index 1d6061b..58587a6 100644
--- a/bp2build/python_library_conversion_test.go
+++ b/bp2build/python_library_conversion_test.go
@@ -35,7 +35,7 @@
 func convertPythonLibTestCaseToBp2build(tc pythonLibBp2BuildTestCase) Bp2buildTestCase {
 	var bp2BuildTargets []string
 	for _, t := range tc.expectedBazelTargets {
-		bp2BuildTargets = append(bp2BuildTargets, makeBazelTarget(t.typ, t.name, t.attrs))
+		bp2BuildTargets = append(bp2BuildTargets, MakeBazelTarget(t.typ, t.name, t.attrs))
 	}
 	// Copy the filesystem so that we can change stuff in it later without it
 	// affecting the original pythonLibBp2BuildTestCase